Shortly after entering the pre-k, my son began to vehemently express his dislike of the school, saying things such as: "I want to move to Pluto; "I want to smash (the name of the school)", and (most disturbingly), "I wish I were dead/never born."
I have heard that being the victim of a bully is a common reason why kids this age wish 'they were never born.' Seems to me that your son having this level of anger at the school is a sign of something bad. Not sure what, but what difference does it make? School, at this age, is supposed to be fun. Really!
He doesn't seem to have any trouble seperating from you, and althrough you and your DH aren't great role models of sociability, perhaps your mom and MIL are better at it?
In the end, there is plenty of good reason for some highly gifted people to be unsocial - they have never found a group of people that are enjoyable and safe to be around. You may actually be a very social person, but have made a decision quite early that most people are boring and dangerous, and so, gotten in the habit of being closed mouthed. Try hanging out here and seeing if you have an undiscovered side to yourself! Or you might just be happy with your own company and that's good too!
Smiles and Welcome,
Grinity